The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.     
If a young man's low testosterone is a problem for a couple trying to get pregnant , gonadotropin injections may be an option in some cases. These are hormones that signal the body to produce more testosterone. This may increase the sperm count. Hedges also describes implantable testosterone pellets, a relatively new form of treatment in which several pellets are placed under the skin of the buttocks, where they release testosterone over the course of about three to four months. Injections and nasal gels may be other options for some men.
There are solutions. Some men don't experience much of a crisis anyway, they just continue living through the first part of their life and into the second. Others go through a period of great turbulence but then find a new course and approach for the second passage of their lives. This may involve a new set of challenges, a new direction, or a coming to terms with what they have got. Often the new paths are more spiritual and less driven than those of their youth. But a few may succumb to disaster in the form of drug, alcohol and sexual addiction, or spend the rest of their lives drifting around aimlessly in a state of depression. The book by Dr Malcolm Carruthers contains vital information on what you can do if this applies to you: "The mid-life crisis, even when it brings on depression, despair, anxiety or fear, is a time of great challenge, out of which come symbols of transformation. As we age, we human beings yearn for wholeness. We yearn for parts of ourselves that have been in the dark to find sunlight, and those that were sunburned to find shade. We yearn for the parts that have been underdeveloped to grow, and those that were overdeveloped to be pruned. We yearn for the parts that have been silent to speak, and those that were noisy to be still. We yearn for the parts that have been alone to find companionship, and those that have been overcrowded to find solitude. In short, we yearn to live our unlived lives." Continued on Andropause page 2 - go here! where we examine the sexual consequences of the andropause including erectile dysfunction and delayed ejaculation. Symptoms of the male mid-life crisis and the andropause Your penis seems to have shrunk